The present invention pertains to heavy duty particulate detergent formulations. Specifically the invention provides a method for incorporating relatively large amounts of liquid nonionic surfactants into heavy duty particulate detergent formulations. More specifically, a method for converting liquid nonionic surfactants into free flowing particulate form, suitable for blending with a particulate detergent powder after spray drying, is provided by the invention.
The most commonly used surface active agents in heavy duty detergent formulations are anionic compounds having detersive properties. Typical of these anionic compounds are the higher alkyl mononuclear aromatic sulfonates such as the higher alkyl benzene sulfonates. These synthetic detergents are very effective in removing dirt from textile fabrics when utilized in conjunction with phosphate builders which function to "soften" the water being used and to provide detersive action. However, considerable controversy exists today as to the efficacy of utilizing phosphate compounds in detergent formulations due to their alleged causation of the eutrophication process in lakes, rivers and streams. Although the eutrophication process, wherein an excessive growth of aquatic plant life is promulgated in natural water bodies, is not completely understood, it is alleged that the phosphate compounds present in detergent containing waste water are a prime factor in promoting this phenomenon.
Although nonionic surfactants are not as effective as anionic surfactants in the presence of large amounts of phosphate builders, it has been discovered that when the phosphate content of a detergent formulation is substantially reduced, the nonionic surfactants appear to provide detergency properties that are superior to anionics in the same reduced phosphate content formulation. Apparently the detersive effectiveness of nonionic surfactants is effected much less by water hardness than that of the commonly used anionic surfactants. In the event that the phosphate builders are totally or partially removed from detergents, the incorporation of progressively larger amounts of nonionic surfactants into detergent formulations may become very desirable.
At present, small amounts of nonionic surfactants are added to detergent formulations, primarily to reduce the amount of foam generated during the washing cycle. The most commonly used nonionic surfactants are ethoxylated long carbon chain alcohols. Typically, the nonionic ethoxamer used has a 12 to 18 carbon atom alkyl chain and an average of about 10 to 19 ethylene oxide units. The range of ethylene oxide content that provides the greatest detergency in these surfactants usually results in a nonionic material that is a viscous liquid at room temperature and therefore unsuitable for direct addition to the dry detergent powder. However, it has been found that when a substantial amount, typically above 5% by weight, of nonionic surfactant is incorporated into the detergent slurry before spray drying, a significant air pollution problem is encountered. This problem, known in the industry as "pluming", is manifested as dense black smoke being discharged from the spray tower.
The primary objective of the present invention is to provide a method for converting liquid nonionic surfactants to dry free flowing form so that they may be readily post added to spray dried detergent formulations to thereby significantly increase the nonionic surfactant content of the final detergent product. The maximization of the nonionic surfactant content of the post addable free flowing powder and the selection of particularly suitable carriers for the liquid nonionic materials are important further objectives of the invention.